Upon submit, the form shows that error above the thank you message. I tried to put the debugger on it and seems like the first email it tries to send fails (email to staff), but the second email goes out without any problem (confirmation email to user). If I drag and switch the two emails around so that it sends out the confirmation email first, still the first email (confirmation email) fails and the second email (email to staff) goes out without any issue. Please see debugger info below (all private/critical info has been replaced)

I strongly recommend that you do *not* use the Dynamic From Email element in your Email Setups. Using this often results in your emails being marked as spam and dropped into a spam filter. Instead use the static From Email with an address that matches the site domain name and use Dynamic ReplyTo Email for the user email. The result is the same but with a much better chance of good delivery.

Sorry, it was a mistake on my part when I replaced the values on the debugger data with generic values. Confirmation emails going to the public users are being sent from our DoNotMail email address and notification emails going to staffs are being sent from web.contacts with a reply to address of the user's email address. The correct values should be as below

Just tested it and the error went away. Having a different Reply To email is causing the form to not send the email. I think we need to switch back to SMTP (used to work even with a different reply to using SMTP) but our server is having issues with Office 365 SMTP recently.